The emigration of neutrophils (Pmns) and monocytes is one of the fundamental events in inflammation. These cells are intimately involved in the elimination of harmful microbes, toxins, and denatured proteins and in the immune reaction to foreign antigens. Pmns are the predominant cell in the acute inflammatory stage, whereas monocytes are found in the chronic stage. The stimulus that mediates the second wave of inflammation resulting in the migration of monocytes into an area has not yet been elucidated. The hypothesis proposed in this study is that this influx of monocytes is in part due to the liberation of a chemoattractant from the neutrophil itself, either following the death of the neutrophil or subsequent to degranulation. The validity of this hypothesis will be determined by the following specific aims. Aim 1, to demonstrate that a naturally occurring cationic granule protein of human Pmns of Mr 37000D (CAP37) has potent chemotactic activity specific for human monocytes, as measured by the modified Boyden chamber technique, and to ask what other responses CAP 37 induces in human monocytes. Aim 2, to determine the amino acid sequence of CAP 37 and the cloning and sequencing of its structural gene so as to define the domains responsible for chemotactic activity. Aim 3, to ask if monocytes have specific receptors that mediate chemotaxis. With radiolabeled proteins we will attempt to detect and measure the saturable and specific binding sites for CAP37 on human monocytes. Aim 4, to evaluate the role of CAP37 as a monocyte- specific chemoattractant in vivo and to ask what other responses CAP37 may exert on monocytes/macrophages in vivo. The release of lysosomal enzymes, IL-1, tumor necrosis factor, superoxide production, and expression of La (class II MHC protein) will be determined with standard assays. It is believed that through these investigations CAP37 will be demonstrated to cause migration of monocytes and modulate other functions in vivo, and that its effects on the activity of monocytes and macrophages at the sites of inflammation will be determined.